Rate Of Electron Transfer Reaction Research Articles

Wide-Dynamic-Range Control of Quantum-Electrodynamic Electron Transfer Reactions in the Weak Coupling Regime.

Catalyzing reactions effectively by vacuum fluctuations of electromagnetic fields is a significant challenge within the realm of chemistry. As opposed to most studies based on vibrational strong coupling, we introduce an innovative catalytic mechanism driven by weakly coupled polaritonic fields. Through the amalgamation of macroscopic quantum electrodynamics (QED) principles with Marcus electron transfer (ET) theory, we predict that ET reaction rates can be precisely modulated across a wide dynamic range by controlling the size and structure of nanocavities. Compared to QED-driven radiative ET rates in free space, plasmonic cavities induce substantial rate enhancements spanning the range from 103- to 10-fold. By contrast, Fabry-Perot cavities engender rate suppression spanning the range from 10-2- to 10-1-fold. This work overcomes the necessity of using strong light-matter interactions in QED chemistry, opening up a new era of manipulating QED-based chemical reactions in a wide dynamic range.

Excited State Processes in Supramolecular Complexes of Cyclic Dibenzopyrrolopyrrole Isomers with C60 Fullerene.

An approach to modulating the properties of carbon nanorings by incorporating pyrrolo[3,2-b]pyrrole units is of particular interest due to the combined effect of heteroatom and antiaromatic character on electronic properties. The inclusion of units other than phenylene leads to the formation of stereoisomers. In this work, we computationally study how the spatial orientation of monomeric units in the ring affects the properties of cyclic dibenzopyrrolo[3,2-b]pyrroles and their complexes with C60 fullerene. For [4]PP and [4]DHPP, the most symmetrical AAAA isomer is the most stable and forms stronger interactions with fullerene than the isomers where one or two monomeric units are flipped, mostly due to less Pauli repulsion. π-Electron delocalization in the monomeric unit is crucial for directing the electron transfer (from or to nanoring). The energy of excited states with charge transfer depends on the HOMO-LUMO gap, which varies from one stereoisomer to another only for [4]DHPP⊃C60 with aromatic 1,4-dihydropyrrolo[3,2-b]pyrrole units. The rates of electron transfer and charge recombination reactions are relatively weakly dependent of the spatial isomerism of nanorings.

Quantification of electron transfer on carbon nanotubes: Effect of edge defects on electro-oxidation of glycerol catalyzed by platinum

It is still an ongoing challenge to quantitatively determine the number of transferred electrons from carbon supports to metallic catalysts, which is highly related to their catalytic performance. In this work, a facile method combining electrochemical and spectroscopic technologies was proposed to evaluate the electron transfer (ET) reaction rate on carbon nanotubes (CNTs) with defects. Using 7,7,8,8-tetracyanoquinonedimethane (TCNQ) as an electron-accepting molecule, the transferred electrons from CNTs were quantitatively determined through the Beer-Lambert law and coulometric analysis. It was revealed that the edge defects on CNTs are beneficial for the ET reaction rate, due to the lower local work function. Hence, the defective CNTs supported Pt nanoparticles (Pt/d-CNTs) performed the higher activity in the electrooxidation of glycerol, suggesting the influence of the ET ability of d-CNTs on the electronic metal-support interaction. This scenario is supported by density function theory calculation and X-ray photoelectron spectroscopy. Our results pave a new way to the facile evaluation of electronic metal–carbon interaction.

Electron Transfer Rates in Polar and Non-Polar Environments: a Generalization of Marcus' Theory to Include an Effective Treatment of Tunneling Effects.

A multistep kinetic model in which solvent motion is treated in the framework of Marcus theory and the rates of the elementary electron transfer step are evaluated at full quantum mechanical level is proposed and applied to the calculation of the rates of intramolecular electron transfer reactions in rigidly spaced D–Br–A (D = 1,1′-biphenyl radical anion, Br = androstane) compounds, for five acceptors (A) in three organic solvents with different polarity. The calculated rates agree well with experimental ones, and their temperature dependence is almost quantitatively reproduced.

Accelerating electricity power generation and shortening incubation period of microbial fuel cell operated in tidal flat sediment by artificial surfactant anode modification

Microbial fuel cell (MFC) performance improves with the addition of synthetic surfactants and biosurfactants in its medium. However, the excessive presence of surfactants, especially synthetic surfactants, leads to inhibited MFC performance. This study is the first investigation for the performance of an MFC operating in real tidal flat sediment when its anode was modified with synthetic surfactants and biosurfactants. The output power intensity of the MFC was inhibited by anodic modification using sodium cholate (SC) as a biosurfactant. This inhibition was also observed at higher and lower SC concentrations. In contrast, anodic modification using polysorbate 20 accelerated the output power intensity of the MFC. The optimal polysorbate 20 concentration was determined to be 25–50 wt%. Under the optimized anode-modified conditions, a rapid increase in the output intensity was observed 7–10 days after the operation. At the most optimal polysorbate 20 concentration (50 wt%), the exchange current density was estimated to be 405 mA m−2, which was more than ten times higher than that (33 mA m−2) obtained at the unmodified anode. This result was due to increasing an electron transfer reaction rate. In conclusion, this positive effect was caused by the synergistic effects of accelerated microorganism proliferation and electron transfer rates at the anode interface.

Effect of substrates on covalent surface modification of graphene using photosensitive functional group

Abstract Graphene has gained much significance for its potential applications in optics and electronics owing to its unique physical and chemical properties. Nevertheless, its gapless band structure greatly limits its wider application in optoelectronic devices. The present study seeks to explore chemical functionalization as an effective method to tune the properties of graphene. Covalent modification of graphene by aryl diazonium salt of a photosensitive functional group (azobenzene) has been used to achieve this goal. This is based on the fact that graphene is a two-dimensional, atomically thin lattice of sp2-bonded carbon atoms, therefore, its properties can be modulated by modifying the underlying dielectric surface with a self-assembled monolayer resulting in doping control. In the study, a clear difference in the rate of electron-transfer reactions with the photosensitive functional group is shown for monolayer graphene supported on SiO2/Si substrates and organic molecule functionalized SiO2/Si substrates. Graphene supported on SiO2/ Si is more reactive towards functionalization than graphene on organic molecule functionalized surfaces, as shown by Raman spectroscopy. The transport characteristics of functionalized graphene on conventional SiO2/Si substrates as well as substrates modified with organic molecule octadecyltrichlorosilane self-assembled monolayers are also explored and compared.

Probing Interfacial Halogen-Bonding Effects with Halogenated Organic Dyes and a Lewis Base-Decorated Transition Metal-Based Redox Shuttle at a Metal Oxide Interface in Dye-Sensitized Solar Cells

Metal-free bis-cyclopentadithiophene-based molecular sensitizers with varying halogens (Cl, Br, and I) installed at a terminal position in conjugation with the dye frontier molecular orbital π-system are studied in combination with two cobalt redox shuttles (RSs): with and without a nonmetal-coordinated nitrogen atom (pyrazine or pyridine) accessible to the halide-decorated dyes. This systematic study employs UV–vis absorption, cyclic voltammetry, density functional theory calculations, and nanosecond transient absorption spectroscopy to probe the influence of possible halogen-bonding between the dyes and the pyrazine-based RS on electron-transfer reactions and effects on dye-sensitized solar cell performances. The results of this study imply a possible halogen-bonding event occurring between the halogenated dyes and the halogen binding RS with substantial effects on electron-transfer reaction rates.

Sulfur-Containing Analogues of the Reactive [CuOH]2+ Core.

With the aim of drawing comparisons to the highly reactive complex LCuOH (L = bis(2,6-diisopropylphenylcarboxamido)pyridine), the complexes [Bu4N][LCuSR] (R = H or Ph) were prepared, characterized by spectroscopy and X-ray crystallography, and oxidized at low temperature to generate the species assigned as LCuSR on the basis of spectroscopy and theory. Consistent with the smaller electronegativity of S versus O, redox potentials for the LCuSR-/0 couples were ∼50 mV lower than for LCuOH-/0, and the rates of the proton-coupled electron transfer reactions of LCuSR with anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine at -80 °C were significantly slower (by more than 100 times) than the same reaction of LCuOH. Density functional theory (DFT) and time-dependent DFT calculations on LCuZ (Z = OH, SH, SPh) revealed subtle differences in structural and UV-visible parameters. Further comparison to complexes with Z = F, Cl, and Br using complete active space (CAS) self-consistent field and localized orbital CAS configuration interaction calculations along with a valence-bond-like interpretation of the wave functions showed differences with previously reported results ( J. Am. Chem. Soc. 2020, 142, 8514), and argue for a consistent electronic structure across the entire series of complexes, rather than a change in the nature of the ligand field arrangement for Z = F.

The Influence of Spectator Cations on Solvent Reorganization Energy Is a Short-Range Effect.

In this manuscript, we use classical molecular dynamics simulation to explore the origin of specific cation effects on the rates of bulk-phase aqueous electron transfer (ET) reactions. We consider 0.6 M solutions of Cl- and a series of different cations: Li+, Na+, K+, Rb+, and Cs+. We evaluate the collective electrostatic fluctuations that drive Marcus-like ET and find that they are essentially unaffected by changes in the cationic species. This finding implies that the structure making/breaking properties of various cations do not exert a significant influence on bulk-phase ET reactions. We evaluate the role of ion pairing in these specific cation effects and find, unsurprisingly, that model redox anions that are more highly charged tend to pair more effectively with spectator cations than their monovalent counterparts. We demonstrate that this ion pairing significantly affects local electrostatic fluctuations for the anionic redox species and thus conclude that ion pairing is one of the likely sources of rate-dependent cation effects in aqueous ET reactions.

Kinetics of oxidation of antidiabetic drug metformin hydrochloride by vanadium(V) in acidic and micellar medium

The kinetics of oxidation of antidiabetic drug metformin by vanadium(V) have been studied spectrophotometrically under pseudo-first order conditions in aqueous acidic and micellar medium. The observed rate of oxidation is first order with respect to both metformin and H+. The pseudo-first order rate constant is independent of ionic strength and varies inversely with dielectric constant of the medium. The effect of micelles (SDS and TX 100) on such reactions has been investigated. Sodiumdodecyl sulphate (SDS) and iso-octylphenoxy polyethoxyether (TX100) accelerate the rate of electron transfer reaction except for cationic CTAB due to the cloudiness of the reaction mixture. It is a one electron transfer process where vanadium(V)is reduced to vanadium(IV) supported by cyclic voltammetric study. The main oxidation product was identified as metformin N-oxide by FTIR and LCMS method. Activation parameters of such reaction have been calculated and reaction mechanism is suggested. Computational study based on Hartree–Fock method supports the reaction mechanism.

Effect of Molecular Structures on the Charge-Discharge Performance for Organic Redox Flow Battery

Large-scale storage batteries include lithium-ion batteries, sodium-sulfur batteries, lead-acid batteries, and redox flow batteries (RFBs),1-3 and these storage batteries have been used for distributed power systems in various places depending on the size and application. Above all, although RFBs4,5 have technical issues, including energy density lower than that of other storage batteries, and their vanadium content makes them expensive, they have long life and high design flexibility. In addition, they operate at normal temperature and pose no danger of thermal runaway or explosion. Therefore, the advantages of RFBs have been attracting attention as one way to achieve power leveling for renewable energy.More recently, research on alternative technology, such as organic, Ti-Mn,6 or hybrid RFBs,7-9 has become active, and in terms of performance, some alternative RFBs, especially organic RFBs, have become comparable to high-cost vanadium RFBs. One of the greatest features of organic RFBs is that it is possible to increase the energy density by controlling the solubility and redox potential based on molecular design, and pioneering and unique research has been reported so far.10-14 The electron transfer reaction rate of the active material in an organic RFB is larger than that in a vanadium RFB, and the reactivity with the carbon electrode is relatively good. For this reason, continued development of RFBs is expected to provide a new power storage technology that can flexibly cope with being combined with other secondary batteries and hydrogen production technologies. Currently, we are focusing on viologen units and have newly synthesized an assemblage of viologen molecules with relatively high symmetry and a regular structure. We are adopting that concept for active material design and aim at improving RFB performance by increasing both the solubility of the designed viologen assembly and the redox response of the individual introduced viologen molecules. Here, we report the application of this idea to aqueous RFBs using newly synthesized viologen molecular units for an anolyte with a relatively high symmetry and regular structure.[1] B. Zakeri, and S. Syri, Renewable and Sustainable Energy Reviews, 42, 569 (2015).[2] F. Shi, Reactor and Process Design in Sutainable Energy Technology, Elsevier (2016).[3] B. Dunn, H. Kamath, and J. -M. Tarascon, Science, 334, 928 (2011).[4] J. Noack, N. Roznyatovskaya, T. Herr, P. Fischer, Angew. Chem., Int. Ed., 54, 9776 (2015).[5] G. L. Soloveichik, Chem. Rev., 115, 11533 (2015).[6] Y. R. Dong, H. Kaku, K. Hanafusa, , K. Moriuchi, T. Shigematsu, ECS Trans., 69, 59 (2015).[7] Y. Xu, Y. Wen, J. Cheng, G. Cao, Y. Yang, Electrochem. Commun., 11, 1422 (2009).[8] X. Wei, W. Xu, M. Vijayakumar, L. Cosimbescu, T. Liu, V. Sprenkle, W. Wang, T. Adv. Mater., 26, 7649 (2014).[9] B. Huskinson, M. P. Marshak, C. Suh, S. Er, M. R. Gerhardt, C. J. Galvin, X. Chen, A. Aspuru-Guzik, R. G. Gordon, M. J. Aziz, Nature, 505, 195 (2014).[10] B. Yang, L. Hoober-Burkhardt, F. Wang, G. K. S. Prakash, S. R. Narayanan, J. Electrochem. Soc. 161, A1371 (2014).[11] J. Winsberg, C. Stolze, S. Muench, F. Liedl, Martin D. Hager, U. S. Schubert, ACS Energy Lett. 1, 976 (2016).[12] K. Lin, R. Gómez-Bombarelli, E. S. Beh, L. Tong, Q. Chen, A. Valle, A. Aspuru-Guzik, M. J. Aziz, R. G. Gordon, Nat. Energy, 1, 16102 (2016).[13] A. Hollas, X. Wei, V. Murugesan, Z. Nie, B. Li, D. Reed, J. Liu, V. Sprenkle, W. A Wang, Nat. Energy, 3, 508 (2018).[14] T. Janoschka, N. Martin, U. Martin, C. Friebe, S. Morgenstern, H. Hiller, M. D. Hager, U. S. Schubert, Nature 527, 78 (2015).

Mechanism Underlying Electron-Transfer Reactions Involving TEMPO and 4-Hydroxy-TEMPO in Deep Eutectic Solvents

Deep eutectic solvents (DES) such as ethaline are considered low-cost, environmentally-benign and non-toxic electrolytes which possess wide electrochemical stability windows. Therefore, these non-aqueous DES electrolytes are attractive for electrochemical applications such as redox flow batteries. However, key drawbacks in applying DES electrolytes include their high viscosities (manifesting in sluggish transport) and sluggish electron-transfer reaction rates [1]. Additionally, mechanistic insights into electron-transfer reactions involving redox-active organic species added to a DES medium are presently unavailable. In this presentation, we report experimental and modeling investigations into the electrochemical oxidation of TEMPO [(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl] and 4-Hydroxy-TEMPO in ethaline DES. Specifically, we present evidence that electrochemical oxidation of TEMPO or 4-Hydroxy-TEMPO involves a two-stage process in which electron transfer is followed by adsorption of the oxidized molecules which either block the electrode surface or gradually desorb and diffuse away into the electrolyte. Mathematical modeling of this two-stage process allows quantitative analysis of experimental polarization curves and cyclic voltammograms. Furthermore, electron-transfer associated with aforementioned organics in DES is compared to and contrasted with analogous processes in aqueous electrolytes to gain additional insights into the proposed ‘adsorption-reaction-desorption’ mechanism. Reference: [1]. Shen. D., Vukmirovic. M. B. and Akolkar. R. 2019 J. Electrochem. Soc. 166 E526.

Pd-Catalyzed Cross Coupling Strategy for Functional Porphyrin Arrays.

Porphyrin arrays are an important class of compounds to study interporphyrin electronic interactions that are crucial in determining the rates of energy transfer and electron transfer reactions. When the electronic interactions become stronger, porphyrin arrays exhibit significantly altered optical and electronic properties owing to large oscillator strength and flexible electronic nature of porphyrins. In addition, porphyrins accept various metal cation in their cavities and the interporphyrin interactions depend upon the coordinated metal. With these in the background, porphyrin arrays have been extensively explored as sensors, multielectron catalysts, photodynamic therapy reagents, artificial photosynthetic antenna, nonlinear optical materials, and so on. Here, we review the synthesis of porphyrin arrays by palladium-catalyzed cross-coupling reactions, which are quite effective to construct carbon–carbon bonds and carbon–nitrogen bonds in porphyrin substrates. Palladium-catalyzed cross coupling reactions employed so far are Suzuki–Miyaura coupling reaction, Sonogashira coupling reaction, Buchwald–Hartwig amination, Mizoroki–Heck reaction, Migita–Kosugi–Stille coupling reaction, and so on. In each case, the representative examples and synthetic advantages are discussed.

Photoinduced Electron Transfer Reactions of tris(4,4’-dimethoxy-2,2’-bipyridyl)ruthenium(II)cation with Quinones in Aqueous Medium

Photoinduced electron transfer reactions of [Ru(dMeObpy)3] 2+ complex with quinones have been studied in aqueous medium by luminescent quenching technique. The complex shows an absorption and emission maximum of 448 nm and 608 nm respectively in aqueous medium. It has an excited state lifetime of 232 ns. The quenching rate constant kq is sensitive to the nature of the quencher and the electron transfer distance between the luminophore and the quencher, the reduction potential of the quinones. The nature of quenching is confirmed from ground state absorption studies. The oxidative nature of quenching is confirmed from the formation of Ru 3+ ion and quinone anion radical. Structural effects also influence the rate of electron transfer reaction.

Photoinduced reactions between naphthoquinone and N,N,N′,N′-tetramethyl-p-phenylenediamine in the mixture of ionic liquid [BPy][NTf2] and acetonitrile studied by transient spectroscopy

Effects of the pyridinium ionic liquid N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide ([BPy][NTf2]) on the photolysis behaviors of 1,4-naphthoquinone (NQ) in the acetonitrile solutions have been investigated by using nanosecond transient absorption techniques. When [BPy][NTf2] existed in the solution, the triplet 3NQ⁎ decayed more slowly and its half lifetime became longer. The photoinduced electron transfer rate constants of NQ and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in the presence of [BPy][NTf2] were lower than those measured in acetonitrile, but of the same order of magnitude as estimated diffusion controlled rate constant. This finding suggests that [BPy][NTf2] could act as an appropriate solvent for electron transfer reactions. The photoinduced electron transfer reaction rate was determined not only by the viscosity but also by the microstructure of the solvent.

Controlling the nonadiabatic electron-transfer reaction rate through molecular-vibration polaritons in the ultrastrong coupling regime

Recent experiments showed that the chemical reaction rate is modified, either increased or decreased, by strongly coupling a nuclear vibration mode to the single mode of an optical cavity. Herein we investigate how the rate of an electron-transfer reaction depends on the molecule-cavity coupling in the ultrastrong coupling regime, where the coupling strength is comparable in magnitude with both the vibrational and the cavity frequencies. We found two main factors that determine the modification of the reaction rate: the relative shifts of the energy levels induced by the coupling and the mixing of the ground and excited states of molecular vibration in the ground state of the hybrid molecule-plus-cavity system through which the Franck-Condon factor between the initial and final states of the transition is altered. The former is the dominant factor if the molecule-cavity coupling strengths for the reactant and product states differ significantly from each other and gives rise to an increase in the reaction rate over a wide range of system’s parameters. The latter dominates if the coupling strengths and energy levels of the reactant and product states are close to each other and it leads to a decrease in the reaction rate. The effect of the mixing of molecular vibrational states on the reaction rate is, however, suppressed in a system containing a large number of molecules due to the collective nature of the resulting polariton, and thus should be observed in a system containing a small number of molecules. In contrast, the effect of the relative shifts of the energy levels should be essentially independent of the number of molecules coupled to the cavity.

Energy and electron transfer reactions on silica gel and titania\u2013silica mixed oxide surfaces

The energy and electron transfer reactions of anthracene co-adsorbed with an electron donor on silica gel and titania–silica mixed oxides have been studied by a combination of steady-state reflectance, emission spectroscopy, and nanosecond diffuse reflectance laser flash photolysis. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been measured; kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene loading. The rate of energy and electron transfer reactions increases as a function of azulene loading and decreases with increasing titania content in titania–silica mixed oxides. These findings indicate that the observed rate of reaction is determined by the rate of diffusion of anthracene on the titania–silica surfaces, whereas, in contrast, the observed rate of reaction on silica gel is predominantly governed by the rate of diffusion of azulene.Graphic abstract

Effect of acid and ionic strength on the kinetics of electron transfer reaction of n-(2-hydroxy-ethyl) ethylenediamine-n, n’, n’-triacetatocobaltate (ii) complex with hypochlorite ion in aqueous acidic medium

The influence of acid and ionic strength on the rate of electron transfer reaction of N-(2-hydroxy-ethyl)ethylenediamine-N,N’,N’-triacetatocobaltate(II)(hereafter, complex with Hypochlorite ion in aqueous nitric acid medium have been studied at I = 0.2 mol dm-3(NaNO3), [H+] = 1 × 10-2 mol dm-3, , T = 300 ± 1 K and λmax = 525 nm. Stoichiometric study showed 1:1 `mole ratio. The rate law derived from the kinetic study under pseudo first order condition is . The rate constant of reaction,  varies inversely with acid concentration, [H+]. The overall rate law is therefore represented as: . The reaction displayed positive salt effect which suggests the activated complex was made up of similar charged species. The reaction was catalysed by addition of formate, HCOO- and potassium, K+ ions and the Michaelis-Menten’s plot gave zero intercept indicating the absence of intermediate complex. A reaction mechanism via an outer-sphere pathway is proposed for this reaction. Â

The photokinetics of phenothiazine dyes with titanium trichloride in different solvents

AbstractThe kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous‐alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first‐order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents.

Donor-acceptor symmetric and antisymmetric tunneling matrix elements: a pathway model investigation of protein electron transfer.

In protein electron transfer reaction rate calculations, the electronic Hamiltonian is apportioned into donor-acceptor (D-A) and protein bridge subspaces, and a two-state system is defined for the D-A subspace. Löwdin partitioning is used to perform the two-state reductions necessary to compute the tunneling matrix element between D and A sites. Here, a method of performing donor and acceptor state analysis for a non-orthogonal basis set in both the weak and strong electronic coupling regimes is developed. The electron tunneling current and coupling are obtained in terms of D-A symmetric and antisymmetric interatomic tunneling elements, and are then used to compare pathway models. These interatomic tunneling elements are both proportional to the Green's function elements of the isolated protein bridge. To facilitate a perturbative treatment of antisymmetric interatomic tunneling currents, we found a well-known expression for the D-A tunneling matrix element in terms of transformed Green's function matrix elements of the isolated protein bridge. Also, the relationship of the tunneling matrix element to BO pathways is discussed using the symmetric interatomic coupling. Finally, the definition of the average interatomic and atomic pathway coupling allows us obtain the quantum interference between interatomic tunneling pathways.